CRT pacing seeks to normalize asynchronous cardiac electrical activation and resultant asynchronous contractions associated with congestive heart failure (CHF) by delivering synchronized pacing stimulus to both ventricles of the heart. The stimulus is synchronized to improve overall cardiac function. This may have the additional beneficial effect of reducing the susceptibility to life-threatening tachyarrhythmias. CRT and related therapies are discussed in, for example, U.S. Pat. No. 6,643,546 to Mathis et al., entitled “Multi-Electrode Apparatus and Method for Treatment of Congestive Heart Failure”; U.S. Pat. No. 6,628,988 to Kramer at al., entitled “Apparatus and Method for Reversal of Myocardial Remodeling with Electrical Stimulation”; U.S. Pat. No. 6,512,952 to Stahmann et al., entitled “Method and Apparatus for Maintaining Synchronized Pacing”; U.S. Pat. No. 7,065,400 to Schechter, entitled “Method and Apparatus for Automatically Programming CRT Devices”; and U.S. Patent Application 2008/0306567 of Park et al., entitled “System and Method for Improving CRT Response and Identifying Potential Non-Responders to CRT Therapy.”
CRT usually involves pacing from the right ventricular (RV) apex, the transvenous LV, typically in the lateral or postero-lateral vein, and the right atrium (RA). Recent studies have suggested that biventricular (BiV) pacing from two LV sites results in an improved clinical outcome in CRT patients, likely due to improved hemodynamic response from dual-LV pacing, in comparison with conventional BiV pacing. A study conducted by Leclercq et al., referred to as the TRIP-HF study (Leclercq et al., “A randomized comparison of triple-site vs. dual-site ventricular stimulation in patients with CHF” JACC 2008; 51:1455-62), demonstrated that CRT with one RV and two LV leads was safe and associated with significantly more reverse remodeling (as assessed by LV ejection fraction (EF) and LV end-systolic volume/diameter) than conventional BiV stimulation. A study conducted by Lenarczyk et al., “Mid-term outcomes of triple-site vs. conventional cardiac resynchronization therapy: A preliminary study,” Intern. Journal of Cardiology 2009; 133:87-94, has shown that after three months of CRT, triple-site (TRIV) pacing was associated with a more significant New York Heart Association (NYHA) class reduction, increase is VO2 max and six-minute walk distance than conventional CRT. The response rate in the TRIV group was 96.3% vs. 62.9% in the conventional group, and TRIV stimulation was found to be an independent predictor of response to CRT. Moreover, Niazi et al., “Dual-site left ventricular stimulation provides better resynchronization response than conventional biventricular stimulation” Heart Rhythm 2006; 3(5):S88 have shown that CRT with simultaneous dual LV site pacing produced a significantly larger increase in maximum change in LV pressure (dP/dtMax) compared to BiV CRT with a single LV site pacing. Rosenberg et al., “Simultaneous Linear Multisite LV Stimulation Improves Hemodynamics Above Conventional BiV Pacing in Dogs with Rapid Ventricular Pacing Induced Heart Failure” Heart Rhythm 2008; 5(5):S136) recently evaluated the hemodynamic effects of multisite LV pacing from a single coronary sinus (CS) branch in a rapid RV pacing-induced HF canine model. They reported that simultaneous MSLV pacing from a single CS branch improves LV hemodynamics compared to single-site LV pacing. In the aforementioned studies, the pulses in the dual-LV pacing were delivered simultaneously with no intraventricular delay (i.e. no LV-to-LV delay).
MSLV pacing systems have been proposed that offer the flexibility of varying an interventricular RV-to-LV pacing delay (RVLV) as well as an intraventricular LV-to-LV pacing delay (LVLV). However, issues can arise when setting these or similar pacing delays. In particular, circumstances can arise where the delays are set too long such that propagation of electrical depolarization wavefronts from other pacing sites can interfere with MSLV pacing. In particular, the depolarization wavefronts can prevent capture of MSLV pacing pulses delivered at sites in the LV or can fuse with events paced at those sites. In either case, inappropriate or ineffective CRT pacing can result. Also, circumstances can arise where the pacing might be proarrhythmic.
Accordingly, it would be desirable to prevent inappropriate or ineffective CRT due to these issues and it is to this end that the invention is primarily directed.